JavaScript - how to measure execution time for each part of a code

You can use console.time('name') and console.timeEnd('name') to measure time between 2 places in your code.

would look something like this:

console.time('part1')   //start timer for part 1.
var mysql = require('mysql');
console.timeEnd('part1')    //end timer 1 and log how long it took.  

console.time('part2')   //start timer for part 2.
var connection = mysql.createConnection({
    host: '...',
    user: '...',
    password: '...'
    port : ...
    database: '...'
});
console.timeEnd('part2')    //end timer 2 and log how long it took. 

console.time('part3')   //start timer for part 3.
connection.connect(function(err) {
  if (err) throw err;
  connection.query("SELECT * FROM table", function (err, result, fields) {
    if (err) throw err;
    console.log(result);
    console.timeEnd('part3')    //end timer 3 in the callback and log how long it took. 
  });
  connection.end();
});

Use console.time(String str) to start a named timer, and console.timeEnd(String str) to end measuring and ouput the time in the console.

function countToThousand(callback) {
  console.time('part1');
  let a = 0;
  for (var i = 0; i < 1000; i++) {
    a += i
  }
  callback(a)
}

function myCallback(a) {
  console.log('a is '+a);
  console.timeEnd('part1')
}

countToThousand(myCallback)

// etc

In case your question is actually "how to know what part of code is sloooow". Tool that makes such a thing is named "profiler".

NodeJS has integrated profiler that can be attached to your IDE(like Inteliji Webstorm)

Or you can search for dedicated package(like v8-profiler) that connects to V8 profiler and draw charts/fill the table with some other package/your own code.

You can use built-in nodejs perf_hooks. For example:

// Dependencies
const { performance, PerformanceObserver } = require('perf_hooks');



performance.mark('start part1');
console.time('part1')   //start timer for part 1.
var mysql = require('mysql');
console.timeEnd('part1')    //end timer 1 and log how long it took.  
performance.mark('end part1');

performance.mark('start part2');
console.time('part2')   //start timer for part 2.
var connection = mysql.createConnection({
  host: '...',
  user: '...',
  password: '...'
    port: ...
  database: '...'
});
console.timeEnd('part2')    //end timer 2 and log how long it took. 
performance.mark('end part2');

performance.mark('start part3');
console.time('part3')   //start timer for part 3.
connection.connect(function (err) {
  if (err) throw err;
  connection.query("SELECT * FROM table", function (err, result, fields) {
    if (err) throw err;
    console.log(result);
    console.timeEnd('part3')    //end timer 3 in the callback and log how long it took. 
    performance.mark('end part3');

    // Create observer to log out all the measurements
    const obs = new PerformanceObserver((list) => {
      // called once. list contains three items
      const measurements = list.getEntriesByType('measure');
      measurements.forEach((measurement) => {
        console.log(`${measurement.name} ${measurement.duration}`);
      });
    });
    obs.observe({ entryTypes: ['measure'] });

    // Gather all the measurements
    performance.measure('Beggining to end', 'start part1', 'end part3'); // Measure whole function
    performance.measure('Part1', 'start part1', 'end part1'); // Measure the part1
    performance.measure('Part2', 'start part2', 'end part2'); // Measure the part2
    performance.measure('Part3', 'start part3', 'end part3'); // Measure the part3

  });
  connection.end();
});

use this method

 const startTime =new Date().getTime();

//part of the code

const endTime = new Date().getTime();
console.log(`time taken=> ${(endTime - startTime)/1000} seconds`);